The present invention relates to multi-layer combined rigid and flexible printed circuits having flexible printed circuits extending from a rigid circuit board and more particularly to improvements in and the process described in my earlier U.S. Pat. No. 4,800,461 issued Jan. 24, 1989 and assigned to the assignee of the present invention. In my earlier U.S. Pat. NO. 4,800,461, particularly as described in FIG. 5 thereof, a Rigid-Flex circuit board is shown wherein a fiberglass-epoxy rigid section is provided with an opening spanned by a flexible polyimide which is designed to provide flexible leads extending from the rigid portion of the board.
In producing the basic copper-fiberglass/polyimide laminate, difficulties have been encountered in providing a smooth, ripple-free laminate which can be held accurately in the focal plane of a photo-resist exposure system for providing the precise photo image which is subsequently developed in the overall etching process to produce the fine copper leads.